1. Field of the Invention
The present invention relates to a charger used for charging a Ni-Cd (Nickel-Cadmium) battery.
2. Description of the Related Art
Heretofore, a charging device or charger used for charging a Ni-Cd battery has basically been made up of a constant-current circuit. When one attempts to charge the Ni-Cd battery using the charger, a controller of the charger detects a charging current flowing in the Ni-Cd battery and effects control for causing the charging current to reach a predetermined current value corresponding to the rated capacity of the Ni-Cd battery. At this time, an internal voltage of the Ni-Cd battery continuously supplied with the constant charging current gradually increases to reach a predetermined voltage value. Thus, the controller of the charger is activated to complete the charging of the Ni-Cd battery.
However, when the Ni-Cd battery is left unused for a long period of time, the electromotive force of the Ni-Cd battery is reduced. The Ni-Cd battery whose electromotive force has been reduced in this way has a high electric resistance and needs a high voltage to cause the charging current to flow in the Ni-Cd battery by the constant-current type charger. However, a problem arises in that when the high voltage is continuously supplied to a Ni-Cd battery that has been left for a long period, the Ni-Cd battery generates heat due to its high electric resistance, causing the Ni-Cd battery to deteriorate.